No prior art search was conducted on the subject matter of this specification in the U.S. Patent and Trademark Office or in any other search facility. We are unaware of any prior art more relevant to the subject matter of this disclosure than that which is set forth below. U.S. Ser. No. 265,316, filed May 20, 1981, entitled "Methods of Monitoring a Combustion System", is assigned to Ford Motor Company, the assignee of the present application. The 265,316 application set forth methods of monitoring a combustion system which were developed before the method set forth in this specification. Included among the many methods set forth in the aforementioned application is a method of measuring the air to fuel ratio of an air/fuel mixture being supplied to a combustion process. The entire Ser. No. 265,316 application is hereby incorporated by reference.
The method of obtaining the air/fuel ratio of an air/fuel mixture being supplied to a combustion process as taught in the aforementioned Ser. No. 265,316 specification is fairly complex because it is a versatile instrument capable of other combustion related measurements. The present specification teaches a method which is less sophisticated than the method taught in the prior application. The method taught in the present specification does, however, give one an excellent indication of the air to fuel ratio of an air/fuel mixture being supplied to a combustion process. However, the method taught in the present specification is not capable of measuring other engine parameters taught in the previous method.
The more complex method of measuring the air to fuel ratio of air/fuel mixture being supplied to a combustion process as taught in the prior specification Ser. No. 265,316 is generally carried as follows. An air/fuel mixture is continuously passed through a combustion process to generate a first stream of gaseous material. This first stream of gaseous material may contain (a) unburned fuel, (b) partially oxidized fuel, (c) carbon monoxide, (d) carbon dioxide, (e) water vapor, (f) nitrogen, (g) oxygen, (h) inert gases normally found in air, or (i) a mixture of any or all of (a) through (h). A sample portion of the first stream of gaseous material is continuously withdrawn into a volume at a first pressure below atmospheric pressure. The first pressure below atmospheric pressure is a pressure that at the temperature of the sample portion continuously withdrawn the water vapor contained therein will not condense. The sample portion continuously withdrawn forms a second stream of gaseous material that has the same compositional makeup on a volume percentage basis as the first stream of gaseous material but at a reduced pressure.
A controlled source of oxygen addition is continuously provided to the second stream of gaseous material. The controlled source of oxygen addition is continuously controlled by application of a control signal thereto. The control signal is applied in a manner that the oxygen is added to the second stream of gaseous material at a rate proportinal to the strength of the control signal applied to the controlled source of oxygen addition. The control signal is continuously developed to a strength which results in the controlled source of oxygen addition adding to the second stream of gaseous material sufficient oxygen that there is after oxygen addition a predetermined amount of oxygen in excess of that required to stoichiometrically oxide any (a) unburned fuel, (b) partially oxidized fuel, and (c) carbon monoxide to (d) carbon dioxide and (e) water vapor.
A sample portion of the second stream of gaseous material is continuously withdrawn into a volume at a second pressure substantially below the first pressure. The sample is withdrawn after the oxygen has reacted with (a) unburned fuel, (b) partially oxidized fuel, and (c) carbon monoxide. This second pressure is a pressure that, at the temperature of the sample portion continuously withdrawn from the second stream of gaseous material, the water vapor contained therein will not condense. The sample portion continuously withdrawn forms a third stream of gaseous material that has the same composition makeup based on fully oxidized carbon and hydrogen on a molar basis as the second stream of gaseous material plus added oxygen but at a reduced pressure.
The third stream of gaseous material is continuously subjected to analysis by a mass spectrometer to generate on a continuous basis an output signal. The output signal developed is indicative of the ratio of oxygen to nitrogen in the third stream of gaseous material. The control signal for application to the controlled source of oxygen is continuously generated from the output signal generated by the mass spectrometer. The control signal strength is generated in a manner that: (1) when the oxygen signal of the third stream of gaseous material being measured by the mass spectrometer is at a predetermined level, the control signal strength has a predetermined strength which ensures the predetermined amount of oxygen in excess of that required to stoichiometrically oxidize the components is added to the second stream of gaseous material; and (2) when the oxygen signal of the third stream of gaseous material being measured by the mass spectrometer falls away from the predetermined level, the control signal has a strength that ensures an amount of oxygen greater than the predetermined amount of oxygen is added to the second stream of gaseous material.
In this manner, the measured oxygen signal is returned to the predetermined level, the instantaneous amount of oxygen being added to the second stream of gaseous material being a direct measure of the air to fuel ratio of the air/fuel mixture being burned in the combustion process.
As is readily apparent, the methodology of the Ser. No. 265,316 specification is rather sophisticated, the sophistication giving rise to an extremely accurate measurement by the method steps of the air to fuel ratio of the air/fuel mixture being burned in the combustion process.
It is a principal object of this invention to provide a method of measuring the air to fuel ratio of an air/fuel mixture being supplied to a combustion process which is relatively simple to carry out, but yet which provides an accurate measurement of the desired parameter.
It is another object of this invention to provide a method of measuring the air to fuel ratio of an air/fuel mixture which can be carried out by instrumentated apparatus of relatively simple design and construction.